In this paper a new ribbed bracing system (RBS) is proposed capable of performing as a variable stiffness system that can be used for controlling structural deformations and frequency shifting to compensate seismic energy. RBS has two important advantages. Because of ribbed system, the compressive member is rigidly moved like a piston and a cylinder and therefore it is a buckling prevented system. Also it is possible to use this system as a semi-active system by considering the story drifts and global structural damage and control the system if it is necessary to be open or closed based on the operational criteria assigned in the system. RBS has no need to any actuator and large power supply, but just a battery-size power supply to switch the ribbed mechanism to be on or off. RBS is composed of a ribbed supplemental part and a normal wind-bracing on each floor. Considering an appropriate criterion based on the storey drift, minimum number of bracing systems will be active on the height of structure during earthquake. In contrast with completely closed RBS (CC-RBS) by on-off bracing system arranged along the height of the building cause period shifting of the structure to the larger value. Three stages are considered in the numerical studies: conventional bracing frame (CBF), CC-RBS and semi-active RBS (SA-RBS). Damage indices and Fourier transforms are calculated in order to discuss on the efficiency of the proposed system. Nonlinear dynamic analysis of system has been carried out and structural behaviour has been investigated.Numerical results show the efficiency of CC-RBS in reducing structural damage and improving seismic energy. Also base shear is reduced when SA-RBS is used and structural damage is more uniform in this case.

Setback in elevation of a structure is a special irregularity with considerable effect on its seismic performance. This paper addresses multistory Reinforced Concrete (RC) frame buildings, regular and irregular in elevation. Several multistory Reinforced Concrete Moment Resisting Frames (RCMRFs) with different types of setbacks, as well as the regular frames in elevation, are designed according to the provisions of the Iranian national building code and Iranian seismic code for the high ductility class. Inelastic dynamic time-history analysis is performed on all frames subjected to ten input motions. The assessment of the seismic performance is done based on both global and local criteria.Results show that when setback occurs in elevation, the requirements of the life safety level are not satisfied. It is also shown that the elements near the setback experience the maximum damage. Therefore it is necessary to strengthen these elements by appropriate method to satisfy the life safety level of the frames.

Construction of welded moment resisting connection is common. These connections have high potential for brittle failure of welds if quality of welding is not controlled. In this research new bolted bracket connection similar to Kaiser bolted bracket connection is introduced. Kaiser connection has invention patent so construction society can’t utilize them without authority. Proposed connection of this paper can be manufactured by both casting and welding methods and can eliminate patent problems. In this evaluation connection performance, pretention force of bolts, height of bracket, number of bolts and length of bracket have been evaluated. In modeling of connection in order to accuracy of results between different connected area and bolts faces contact elements were created. The standard cyclic history was selected for loading of specimens. The results shows that proposed connection can be accepted by connection code for using in special moment resisting frames from both ductility and strength aspects. Findings are extended as hysteresis curves, released energy of connection, rupture index indicators and slip of bolts.

The seismic performance of hybrid braces composed of steel and shape memory alloy (SMA) was investigated in this paper. Six types of hybrid braces were used, constituted by SMA content of 0, 20, 40, 60, 80, and 100%. A nonlinear dynamic analysis was performed under El Centro earthquake records, with the maximum acceleration of 0.6g and 0.9g. Our results showed that the seismic performance, i.e., the amount of energy absorption and residual strain, of steel–SMA hybrid braces depends on the SMA content. The optimal value of SMA content was 20%, as, at this concentration, a hybrid brace can be designed with good seismic performance at a justifiable fabrication cost.

Pullback test has no scrupulous theoretical establishment. It is based on the hypothesis that the response of the structure can be related to the response of an equivalent single degree-of-freedom (SDOF) system. This implies that the response is controlled by a single mode. In fact, the steel frame of each safe room, which is introduced within the unreinforced masonry buildings for protecting the lives of residents in catastrophic earthquake failures, contains a SDOF structural system. In pullback test, the steel frame carries its gravity load first, and then it will be pushed under an incremental lateral roof displacement pattern, which is imposed to its center of mass. This paper expresses the results of 13 pullback tests executed by the authors on the steel frames of safe rooms. The results show that pullback test is a practical method for seismic performance evaluation of safe rooms. Also the performance of these frames located in a collapsing three storey masonry building is presented with favorable conclusions. In fact, the results of pullback test of the safe room located at the ground-floor level were compared with the requirements of Iranian code for seismic resistant design and it was concluded that the steel frame had an acceptable performance against seismic effects.